An adjustable pit-mounted dockboard includes a ramp having its rear end hinged to the supporting structure or frame, and the ramp is movable from a generally horizontal cross traffic position to an upwardly inclined position. Hinged to the front edge of the ramp is an extension lip which is adapted to swing from a pendant position, in which the lip hangs downwardly from the front edge of the ramp, to an extended position in which the lip forms an extension to the ramp. The lip, when in the extended position, is adapted to engage the bed of a truck or carrier located in front of the dock and bridges the gap between the ramp and a truck bed to enable material handling equipment to move between the dock and the truck.
In an upwardly biased-type of dockboard, the ramp is biased upwardly to the inclined position by a spring assembly, and a manually releasable holddown mechanism is employed to hold the ramp against upward movement. The holddown mechanism is a uni-directional device which prevents upward movement of the ramp through the force of the spring assembly, unless released, while permitting free downward movement of the ramp.
With an upwardly biased type of dockboard, the ramp, when in the upwardly inclined position, must be walked down by the operator in order to engage the extended lip with the truck bed. To walk down the ramp, the operator moves outwardly on the ramp and the weight of the operator, in combination with the weight of the ramp, will overcome the biasing action of the spring assembly so that the ramp is lowered until the lip engages the truck bed.
A second common type of dockboard is a downwardly biased or nose-heavy board in which the weight of the ramp will move the ramp downwardly. A downwardly biased dockboard requires an auxiliary force to move the ramp from the cross traffic position to the upwardly inclined position, and this auxiliary force can take the form of hydraulically operated cylinders, truck actuated linkages, or the like. With the ramp elevated, the auxiliary force is removed, and the ramp will descend by gravity until the extended lip contacts the truck bed.
A downwardly biased dockboard has an advantage in that no holddown mechanism is required, as used in an upwardly biased dockboard, and the loading at the hinge connection of the ramp to the dock or frame is reduced. Furthermore, the ramp will descend by gravity and downward movement of the ramp is not subject to the varying weight of the operator.